Occurrence of disordered magnetic moments at the Si(111) unreconstructed surface

The evolution of the magnetic properties of the Si(111)-(1 × 1) surface with temperature is examined. It is shown that the low-temperature antiferromagnetic state is first followed for $T>\mathrm{}{T}_N$ by a disordered magnetic state and then at higher temperatures by a paramagnetic state. The critical temperatures are calculated, and it is found that the disordered magnetic state is likely to be the observed one in the usual temperature range. The experimental consequences of this finding are discussed.